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PA10315 COPY > Synapses > Flashcards

Synapses Flashcards

1
Q

What are graded potentials

A
  1. Graded potentials are activated by synapses from other neurons
  2. Above threshold action potentials are generated
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2
Q

Describe nerve cell communication

A
  1. Action potentials are generated in presynaptic neurone by graded potentials activated by inputs from other neurones
  2. Invade synaptic terminals after propagation
  3. Release chemical synaptic transmitter
  4. Generate graded potential in postsynaptic neurone
  5. Postsynaptic potential can be inhibitory or excitatory
  6. Some neurones communicate via electrical junctions
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3
Q

What are the two types of synapse

A
  1. Chemical

2. Electrical

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4
Q

Describe electrical synapses

A
  1. Electrical synapses- gap junction
  2. Formed by connexons in both cell membranes
  3. Direct passage of ions and small molecules through channel
  4. Permit very rapid faithful transfer of signals
  5. Pre- and post-synaptic neurones are directly connected by gap junctions (2 nM)
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5
Q

Describe chemical junctions

A
  1. Pre- and post-synaptic neurones are physically separated by synaptic cleft around 30 nm (20-50 nM)
  2. Presynaptic neurones release chemical transmitter from their axon terminals
  3. Transmitter binds to receptors on post-synaptic neurons
  4. No physical connection
  5. Chemical released passes to receptors by diffusion across the gap
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6
Q

What are axodendritic synapses?

A

Between the axon of one neurone and the dendrites of another.

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7
Q

What are axosomatic synapses?

A

Between the axon terminals of one and the cell body of another.

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8
Q

What are axoaxonal synapses?

A
  1. Between two axons.

2. another synapses can influence transmission by touching the terminal of another synapse

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9
Q

Describe the shape of CNS synapses

A
  1. Presynaptic terminals contain vesicles arranged at active zones
  2. Postsynaptic membrane is specialised and contains clusters of neurotransmitter receptor and signalling molecules
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10
Q

What are the two types of neurotransmitter receptors?

A
  1. Ligand-gated ion channels

2. G-protein coupled receptors.

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11
Q

What must a Neurotransmitter be

A
  1. present in axon terminals -presynaptic terminals- along with synthetic material for making it
  2. When a stimulus comes released in response to depolarisation (calcium dependent exocytosis)
  3. Specific receptors in post membrane mechanism to mediate postsynaptic response
  4. Have to show there is a mechanism to get rid of it-
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12
Q

Describe how are ligand-gated channels opened?

A
  1. The neurotransmitter binds to the receptor
  2. activated resulting in a conformational change such that it forms an open channel
  3. channel ionotropic receptor
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13
Q

How are G-protein coupled receptors opened?

A
  1. bind to transmitter don’t have ion channel
  2. G-protein bind to receptor and then binds to effector protein which sends intracellular messages to a voltage-gated ion channel so that it opens.
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14
Q

Where does Ach act?

A
  1. nicotinic (ion channels)

2. muscarinic (G protein coupled) receptors.

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15
Q

How is Ach synthesised

A
  1. ACh is synthesised in the presynaptic axon by the enzyme choline acetyltransferase (ChAT)
  2. Choline and acetyl CoA combining.
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16
Q

How is Ach degraded

A
  1. acetylcholinesterase (AChE) in the cleft

2. Choline and acetic acid.

17
Q

What is Cholinergic transmission

A
  1. A ‘model’ synapse
  2. The synapse between motor neurones and skeletal muscle
  3. Soma of motor neurone in CNS can be 1 metre from terminals in muscles
  4. Junction known as motor endplate
  5. Uses Ach as transmitter acting at nicotinic receptors, in same way as CNS synapses.
18
Q

Where does Ach come from

A
  1. Comes from diet and from being reused

2. Not major transmitter in brain

19
Q

Why are neuromuscular junctions used as a model synapse?

A

They are easy to experiment with and study - they are simple as there is only one input and one output.

20
Q

What are the brains main neurotransmitters

A
  1. Amino acids are the main brain neurotransmitters
21
Q

What are two example of amino acid neurotransmitters

A
  1. Glutamate

2. GABA

22
Q

Describe glutamates role

A
  1. The main excitatory transmitter in the CNS
  2. Activates a large number of both ionotropic and metabotropic receptor
  3. glutamate generates an excitatory postsynaptic potential (EPSP)
23
Q

Describe GABA roles

A
  1. The main inhibitory transmitter in CNS
  2. Activates small family of ionotropic and metabotropic receptors
  3. g-aminobutyric acid (GABA) generates an inhibitory postsynaptic potential (IPSP)
  4. open channel which is permeable to chloride ions
  5. causes hyperpolarisation
24
Q

What is temporal summation

A
  1. adding together potentials that occur at the same synapse but at different times
25
Q

What is spatial summation

A
  1. Adding together potentials that occur at different sites on the nuerone.
26
Q

What are common features of all neurotransmitters

A
  1. presynaptic terminals have vesicles arranged in active zones, with the others dispersed
  2. post membrane is specialised and contains clusters of neurotransmitter receptors and signalling molecules
27
Q

Process of release of neurotransmitter by exocytosis

A
  1. vesicles docked at active sites
  2. arrival of AP causes VGCC to open
  3. calcium ions flow in and allow docked vesicles to fuse with the membrane (some completely fuse and some are recycled by endocytosis)
28
Q

What is needed for action potentials to occur?

A

Graded potentials to reach above the threshold.

29
Q

What can a drug do

A
  1. increase leakage of neurotransmitter from a vesicle
  2. increase transmitter release into cleft
  3. inhibit transmitter synthesis
  4. block transmitter uptake
  5. bind to receptor on post-synaptic membrane to block neurotransmitter (agonist)
  6. inhibit or stimulate secondary messenger in post-synaptic cell

PA10315 COPY (48 decks)

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